1. Field of the Invention
The present invention relates to a coating composition capable of forming a coating film showing a low contamination from early time after coating.
2. Description of Background Art
An outdoor coating composition showing good weather resistance has conventionally be applied onto outdoor substrates such as building structures, displays, guard fences, machines, vehicles and the like for the purpose of decoration or protection. However, the conventionally used outdoor coating composition had such disadvantages that the surface of a coated product may easily be contaminated and show poor appearance by influence of exhaust gas, sand, dust, iron powder, rain, sunlight, etc. during outdoor exposure.
In connection therewith, the present applicant proposed such a coating composition that the addition of an organosilicate and/or its condensates makes it possible to form a coating film having self cleaning properties and hard to be contaminated (see International Publication No. WO94/06870 specification).
However, the above coating composition had such drawbacks that hydrolysis of the organosilicate in the coating film does not easily take place depending on the weather on coating or immediately after coating, resulting in being easily contaminated before developing self-cleaning properties. An initial contamination may disappear with time, but may cause claims from clients, and self-cleaning properties from early time after coating are demanded.
3. Disclosure of the Invention
The present inventors made intensive studies for the purpose of solving the above problems to find out that a coating composition containing specified amounts of an organosilicate and/or its condensate and an acid surface active agent or a boric acid compound can form a coating film showing a low contamination from early time after coating and good interlayer adhesion properties between the coating film and a substrate.
That is, the present invention provides a coating composition containing 0.1 to 50 parts by weight of (A) an organosilicate represented by the general formula: where R is same or different and represents hydrogen atom or monovalent hydrocarbon group having 1 to 7 carbon atoms, and/or its condensates per 100 parts by weight of a resin solid content in the coating composition, and 0.1 to 50 parts by weight of (B) an acid surface active agent or a boric acid compound per 100 parts by weight of a solid content of the component (A).